Many power tools such as power driven drills and screwdrivers include a clutch between the transmission and the output shaft of the power tool. The purpose of the clutch is to reduce or effectively interrupt transmission of torque from the transmission to the output shaft when the torque exceeds a threshold amount. This helps to avoid adverse events when such tools are used, e.g., to insert threaded fasteners, such as stripping of the head or threads of the fastener, fracture of the fastener, cam-out of a screwdriver bit, and over tightening of the fastener.
Examples of certain types of clutches can be found in, e.g., U.S. Pat. Nos. 7,066,691 and 8,251,158, which are incorporated by reference. The clutches disclosed in these patents generally include a clutch ring that abuts against one or more springs. The springs presses one or more locking members (e.g. clutch plates, balls, and/or pins) against a clutch face coupled to a portion of the transmission. When the torque overcomes the force exerted by the spring and the locking members, torque transmission from the transmission to the output spindle is reduced or effectively interrupted.
In some embodiments, the force exerted by the spring, and thus the threshold torque, may be user adjustable. For example, the clutch may include an external adjustment sleeve that is rotatable to move an internal clutch ring to alter an amount of compression of the spring. This may be achieved, e.g., by having the clutch ring be threaded to a portion of the housing. However, a deficiency of such a design is that when the clutch ring rotates, the spring(s) may become twisted, which may reduce their life and/or effectiveness.